The Legal Deposit Libraries Act 2003 (c 28) is an Act of the Parliament of the United Kingdom which regulates the legal deposit of publications in the United Kingdom. The bill for this Act was a private member's bill. This Act was passed to update the legislation on legal deposit to reflect the digital age.
The previous provisions covering legal deposit in the United Kingdom were under the Copyright Act 1911. They covered published paper products of almost all types, excluding only ephemera such as diaries and bus timetables. By the beginning of the 21st century many publications appeared in electronic form, either exclusively or in addition to their print form. A voluntary set of rules for deposit had been drawn up a few years earlier but it was felt that the additional force of statute was required to ensure the British national published record remained complete.
More information on the Wikipedia page